def derivate(self):
        new_data = []
        for i in range(len(self.times)):
            for j in range(len(self.data[i, : ])):
                new_data.append((self.data[i+1, j] - self.data[i,j])/self.times[i+1] - self.times[i])     
        return self.copy(data=new_data)
